6.10.8 Predefined macro names
The following macro names shall be defined by the implementation:
__DATE__
__FILE__
__LINE__
__STDC__
__STDC_HOSTED__
__STDC_MB_MIGHT_NEQ_WC__
__STDC_VERSION__
__TIME__
The following macro names are conditionally defined by the implementation:
__STDC_IEC_559__
__STDC_IEC_559_COMPLEX__
__STDC_ISO_10646__
6.4.2.2 Predefined identifiers
The identifier
__func__shall be implicitly declared by the translator as if, immediately following the opening brace of each function definition, the declaration
static const char __func__[] = "function-name";